1. Field
This disclosure generally relates to a computing environment. More particularly, the disclosure relates to sampling technology.
2. General Background
Either time-based or hardware event-based sampling technology is typically utilized in application profiling tools to determine the specific usage of resources. A current approach is to periodically generate an interrupt to take a sample. When the interrupt is taken, sample data is collected and recorded. Examples of the sample data are the interrupted process/thread, the instruction being executed or, optionally, the data address being accessed at the time of the sample. At a later time the collected data is aggregated, and reports are generated showing sample distribution by address, symbol, process, etc. A variety of tools are based on this technology. The full execution context of the sample is not typically recorded and not available in reports.
Attempts have been made to improve this technology by getting call stacks at the time of the sample. The existing set of tools may either attempt to walk the call stack directly or invoke functions on a separate (sampler) thread to obtain the interrupted thread's call stack. Attempting to walk the call stack at the interrupt level is not ideal, because some applications may have stacks that have been paged out. In addition, stack walking code typically does memory allocations, which are not allowed at the interrupt level. As a result, a user-mode sampling thread may be employed to walk the call stacks when requested. On multiprocessor systems, requesting that a separate thread gather the interrupted thread's call stack may allow the interrupted thread to migrate to a different processor and make forward progress, i.e., continue execution, while the call stack is being gathered. The gathered call stack will not reflect the state of the thread at the time it was interrupted.